3.2 Plant and Animal breeding Flashcards
Why do plant and animal breeders try and develop new and improved varieties of crops and livestock?
to provide sustainable food sources
they do this by manipulating or changing the heredity/genetics of an organism
REMEMBER!
discrete variation - can divide members of a species into distinct groups
continuous variation - changes gradually from one extreme to another
What does single gene inheritance control?
controls characteristics which show discrete variation
what is polygenic inheritance?
characteristics which show continuous variation are controlled by several genes.
characteristics which are controlled by polygenic inheritance can also be influenced by the environment
REMEMBER!
Genetically modified organisms have been reprogrammed by genetic engineering to develop characteristics that are useful to humans
Genetic modification
reason for altering genetics, the benefit and an example
increase in yield - more food produced - barley
increase in nutritional value - increase in protein content - rice
resistance to disease - crop not damaged by disease - blight resistant potatoes
resistance to pests - crop resistant to insect, fungus or worms - soya been resistance
to survive a particular environment - adapted to grow in a hot, dry environment - corn
to make it more suitable for rearing or harvesting - a more uniform crop height makes harvesting easier, increasing yield - wheat
What is a cultivar?
a cultivar is a plant that has been created or selected intentionally for desirable characteristics that can be maintained by cultivation.
A cultivar is different from others in at least one characteristic or trait.
Example of cultivar?
agricultural crops are almost exclusively cultivars
What is a field trial?
an experimental investigation in an organisms natural environment ( rather than in the lab)
Use of field trials?
plant field trials used to see whether a particular treatment makes a difference to the crop
measurements such as height, grain size, yield or incidence of disease can be used to determine the effects of a treatment
Trials can be used to evaluate what?
the performance of different cultivars in a range of environments
the effects of different treatments such as pesticides or fertilisers
genetically modified crops
CHECK NOTES FOR AN EXAMPLE
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What do reliable and valid field trials require?
- careful selection of treatment - if the treatment to be investigated is the effect of fertiliser, the treated plot would be given fertiliser and the control plot would have no fertiliser. all other variables would be kept constant. The treated and untreated plots should be as similar as possible (the same soil moisture and slope) to allow valid comparison of treated and untreated areas.
- replicates - use several trial plots to increase the reliability of results. this reduces the effect of variability within samples.
- randomisation - the treated and control areas should be scattered randomly across the site of the trial to eliminate the possibility of bias when measuring the effect of the treatment
What is a method of increasing food security?
to develop new varieties of crops and livestock breeds using breeding programmes
What do breeding programmes allow?
allow desirable features to be bred into particular plants or animals
what are desirable characteristics that increase food security?
wheat - high grain yield potato - resistance to fungal disease soya bean - high protein content of seeds strawberry - resistance to frost dairy cattle - high milk yield beef cattle - high meat yield
TOPTIP
phenotype - physical appearance of offspring
genotype - alleles (forms of a gene) carried
dominant alleles - show up in phenotypes
recessive alleles - do not show up in phenotype unless there are no dominant alleles present to make them
TOPTIP
an organisms genotype is homozygous when it has two identical alleles of a gene it is true breeding
when it has two different alleles of a gene it is heterozygous
What are dwarf varieties of cereal?
dwarf varieties of some cereal crops with much shorter stems then normal were discovered
these plants put more energy into creating see and were easier to harvest, thus increasing the yield of these crops and improving food security
What is selective breeding?
plant and animal breeders choose the parent organisms with the desired characteristics and use them in their breeding programme
the aim is to produce offspring with the combined characteristics of the two parents
What is outbreeding?
outbreeding is the mating of unrelated or distantly related members of a species.
animals and cross pollinating plants are naturally outbreeding
What is inbreeding?
inbreeding is the mating of closely related individuals
this can happen naturally in self pollinating plants
what are inbreeding programmes?
in inbreeding programmes, selected plants or animals are bred for several generations until the population breeds due to the elimination of heterozygotes
What is inbreeding depression?
inbreeding results in homozygosity leading to the accumulation of harmful (deleterious) homozygous alleles and increasing the chances of offspring being affected by recessive traits - this is inbreeding depression
What can inbreeding depression result in?
loss of vigour and poor general health, reduced fertility or yield
What plants are less susceptible to inbreeding depression?
self pollinating plants since natural selection eliminates the deleterious alleles over many generations
How do breeders avoid inbreeding depression in naturally outbreeding species?
by choosing parents with desired characteristics but which are otherwise genetically diverse
What is crossbreeding?
when a plant or animal is crossed with another organism with a different, but desired genotype, creating offspring with traits from both parents, improving characteristics and producing F1 organisms with hybrid vigour
What are F1 hybrids?
an F1 hybrid is the cultivar derived from two different parent cultivars
e.g. almost all modern cultivars of edible (seedless) bananas are hybrids of two wild banana species with seeds
What are disadvantages of F1 hybrids?
a disadvantage of F1 hybrids is the greater cost of seeds
this is because it can take several years to produce inbred lines and non commercial self-pollination often has to be done manually which is time consuming
What is a crossbreed?
a crossbreed is the result of breeding two different purebred parents of different breeds
Example of crossbreeds?
Scottish half bred sheep
cross between a cheviot and border leicester breeds
has the large body from border leicester and high muscle mass from cheviot
What is mutation breeding?
mutation breeding in plants involves exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to breed with other cultivars
How has mutation breeding improved certain crops?
giving disease resistance, dwarf habit or a change in the chemical or nutritional plant composition
TOP TIP
genetically true breeding animals command higher market prices when sold as breeding stock
What is a testcross?
a testcross is used to determine the genotype of an individual with a dominant phenotype to find out if it is homozygous or heterozygous
the organism with the dominant phenotype is crossed with an organism that is homozygous recessive for the same characteristic
Why can a testcross be used in a breeding programme?
to identify unwanted individuals with heterozygous recessive alleles
DONT FORGET
genetic engineering is the genetic alteration of a cell by insertion of a gene or genes from another organism this cell has been GM modified producing a GM organism
What is a genome?
an organisms genome is the full and unique set of genetic instruction in its DNA
What is genomic sequencing?
is a process which can determine the DNA sequence of an organism’s genome
How is the DNA broken up?
using enzymes
Why are genomic sequencing machines used to sequence the DNA fragments and computer programmes are used?
to compare the overlapping sections to recreate the sequence of the original DNA strand
What is the purpose of genomic sequencing?
allows organism with desirable genes to be identified and used in breeding programmes
What is genetic transformation?
genetic transformation is the alteration of the genome of a cell by the insertion of a gene or genes from another organism, either naturally or artificially
the transformed genome can then be used in breeding programmes
What are GM crops are useful for?
protection from threats such as low temperatures, insects and viruses
increasing nutritional value or yield
increasing tolerance of salt or drought
reducing the need for as much fertiliser or pesticide
What is BT toxin?
the soil bacterium bacillus thuringiensis (Bt) produces a protein (Bt toxin) which is toxic to certain insects
when eaten the toxin is activated and destroys the insect’s gut
there are different strains of BT toxin which are effective against different insect pests
Scientists can remove the BT toxin gene from bacteria and insert it into plants, allowing plants to produce their own toxin which offers protection against damage by insects
this removes the need to use chemical insecticides
What is glyphosphate?
Glyphophate is a herbicide (weedkiller) which is particularly effective against broadleaf weeds and grasses that compete with crops
It us an enzyme inhibitor in the production of amino acids and when absorbed through the plant foliage, it is transported to the growing points of the plant, killing it.
Genetically engineered plants that are glyphosphate tolerant can ow be produced
they contain a glyphosphate resistance gene allowing farmers to control weeds without damaging their crop
What vitamin is low in rice?
Rice is low in vitamin A so in areas where rice is the staple diet vitamin A deficiency and its associated visual defects are prevalent
What can be done to sort this deficiency of vitamin A in rice?
two genes coding for beta carotene can be inserted into the normal rice genome so that rice plants can make beta carotene which allows us to make vitamin A.
What is golden rice?
golden rice is a genetically engineered rice cultivar which contains beta carotene and therefore is yellow-orange in colour
